Transient water hammer on one fixture only

Our 2nd floor shower has intermittent/transient water hammer. It is the only fixture in the house that has it. It starts when the water is turned on, and the pipes rumble like mad. Sometimes it goes away on its own, sometimes you have to turn the water off and then back on again. Seems to happen mostly when the outside temperature is cold, but not 100% sure about that.

How can I diagnose and hopefully fix this problem?

Water hammer occurs when you turn off a valve fast, it cannot happen while the valve is open. A chattering washer can create noise as water flows over it. My unprofessional opinion.

noise

My thought is the same as Jim's.

The washer is loose or it's worn and the outer edge is feathered out, is thin and it flutters.

Sound may go away if faucet is full on.

You must know which faucet you are using, so pull it apart and put new washers on.

Thanks guys. This is a shower valve, part of a tub/shower combination. I'll open up the escutcheon and see what's in there. I'm itching to demo/remodel the whole thing but budget restrictions will probably mean I only put in a new cartridge.